EP1700964 reveals a modular construction system and a method for leveled assembly of prefabricated construction modules. The modular system consists of heavy-duty concrete construction modules to be vertically stacked and placed one next to the other for the construction of, preferably, residential buildings. Each module forms a monolithic structure or consists of a steel frame and panels with walls, roof and floor. The modules include fitting devices for stacking; lateral connection elements between modules and/or horizontal and vertical clamping straps. Modules are leveled using leveling sheets and/or non-shrink mortar and/or a method using jacks and tubular sections filled with non-shrink mortar until it sets and jacks are withdrawn. Each construction module includes all accessories and finish elements for a house, such as facades, windows, installations, furniture and internal equipment.